Deflection of electron beams



Sept. 19, 1950 A. w. FRIEND DEFLECTION OF ELECTRON BEAMS Filed April 30,1948 INVENTOR I flZderZIt Fniend BY ATORNEY Patented Sept. 19, 1950DEFLE'GTION F ELECTRON BEAMS Albert W. Friend, Lawrenceville, N. J.,assignor to Radio Corporation of America, a corporation of DelawareApplication April 30, 1948, Serial No. 24,145

16 Claims. 1

This invention relates to deflection of electron beams, and moreparticularly to an improved deflection method and system which is simpleand economical of apparatus and in operation. Provision is also made forrectification to supply either positive or negative high voltage.

Many known combinations of deflection and high-voltage supply systemsemploy as many as four, five, or more electron tubes, at least two ofwhich must be power tubes, and one of the latter usually is ahigh-impedance pentode, or beam tetrode. The other power tube usually isa damper, which may also act as a voltage-booster tube. In such systemsthe power is applied at an intermediate point in the deflection cycle,then at the end of a trace the power is cut off for retrace and storedenergy is used for the next trace up to near said intermediate point.This results in a crossover point where the stored energy ceases andpower is re-applied, usually to the left of center of the trace path.Inasmuch as the trace should be linear with respect totime, thediscontinuity at the cross-over point presents difliculties.

The present invention avoids such difliculties by applying the powerduring retrace and using stored energy for the entire trace, whichtherefore is continuous and has no cross-over point. The inventionincludes a circuit for accomplishing such result which requires only twotubes, preferably high-current low-impedance power triodes, and they maybe alike. Both triodes may, however, be mounted in one envelope.

Hence, the main object of the present invention is to provide a simplerand more economical deflection system.

Another object is to make the trace continuous and linear with respectto time.

A related object is to obtain a high-voltage, low-current supply fromthe deflection apparatus.

Other objects and advantages of the invention will become apparent fromthe following description in connection with the accompanying drawing inwhich:

Figure 1 is a circuit diagram illustrating one embodiment of theinvention by way of example; and,

Figure 2 illustrates another embodiment thereof. I

In both figures like reference characters indicate similar parts.

Referring to Figure 1, S represents a source of positive synchronizing(sync) pulses which are impressed upon the grid of a power tube Illthrough a coupling condenser II and secondary winding l2 of atransformer indicated generally by reference character l5. The source Sis terminated by a resistance l6 and connected to one side of condenserH and to the cathode of tube Ill. The other side of condenser II isconnected through a resistance H to said cathode, which is grounded. Theanode of tube It is connected to primary winding l8 as its load. Thearrangement thus far described may be the usualblocking oscillatorcircuit for generating a wave (e-l) with sharp negative pulses in theoutput circuit of tube ID, as indicated on Figure 1.

Transformer I5 has a secondary winding 20 across which is connected, inparallel, a winding 2| of an electromagnetic yoke 22 suitable fordeflecting electron beams. This part of the circuit also includes aby-pass condenser 23 for periodic current and a balancing condenser 24which latter may be connected to the mid-point of winding 2| to balancethe distributed capacity of yoke 22 relative to ground.

Across the secondary 2|] and winding 2| there are connected, in series,a second power tube 25 and a storage condenser 26. The anode of tube 25is connected to that end of secondary 20 which is made negative bynegative pulses in primary I8. The cathode of said tube is connected toone side of condenser 26, the other side of which is connected towinding 2] and (for periodic current) through condenser 23 to thepositive end of secondary 20. The grid circuit of tube 25 may be a knownform of linearity network comprising a condenser 28 connected betweenthe anode and grid of said tube, a fixed resistance 29, and two variableresistances 30 and 31 connected in series from grid to cathode of tube25, and a condenser 32 shunting the resistance 3!.

The direct-current anode circuits for tubes'lll and 25 are connected inseries as follows. From the positive terminal B+ of a source of anodevoltage, the anode current passes through a centering device 35 havingtwo variable taps 36 and 31 connected respectively to the ends ofsecondary 20 and yoke winding 2|, forming two parallel paths for theanode current which are joined together at the other ends of saidwindings and connected to the anode of tube 25. The cathode of said tubeis connected by leads 38 and 39 to one end of the transformer primaryl8, the other end of which is connected to the anode of tube Ill aspreviously mentioned. The circuit is com-- pleted by the connection fromthe cathode of tube H] to ground which is also connected to the negativeterminal B of the voltage source. This voltage source and the centeringdevice 35 are bypassed by a condenser 4|.

It may be desirable to connect a variable balancing resistance 52between the cathode lead 38 and the tap 3'! in order to bleed-off anyexcess of average anode current in tube 25 over that in tube l0. OtherB+ loads can be taken from the point 43 of centering device 35 ifdesired.

In order to supply a high negative voltage from the deflection systemthus far described, a highvoltage secondary winding 45 is provided ontransformer I5. Such winding may be a continuation of secondary winding20 as indicated. A part (usually two or a few turns of heavier wire) ofthe high-voltage end of winding 45 is connected across a cathodefilament or heater 46 of a rectifier tube 41, the anode 48 of which isconnected to a filter condenser 56. The other side of condenser 50 maybe connected to the grid end of winding l2, as shown, or in some casesto 3+ or to ground. The rectified high voltage may be supplied through alead and high resistance 52 to the cathode 53 of an image tube 55, suchas a kinescope. The second anode 56 thereof may be connected to asuitable point of relatively positive potential such as B+ or ground.

The circuit of Figure 2 is the same as Figure 1 as far as the deflectingsystem is concerned, but the transformer I5 and rectifier tube 4! arearranged to provide a positive high voltage for the tube 55. Thisarrangement requires a separate winding 51 for heating the cathode 46 ofthe rectifier. Said cathode is connected to the positive side ofcondenser 50, the negative side of which is connected to that end oftransformer winding 20 which is negative when the primary pulses arenegative. The positive end of winding 20 is connected to the negativeend of highvoltage winding 45, the positive end of which is connected tothe anode 48 of the rectifier. The positive high voltage is taken fromthe cathode 46 through lead 5! and high resistance 52 to supply thesecond anode 56. In this case the cathode 53 may be grounded.

It is understood that yoke 22 and winding 2| are assembled with imagetube 55 so as to deflect the electron beam from cathode 53 in knownmanner.

The deflection system shown in Figures 1 and Zoperates as follows.Starting of the anode current drives the grid of tube [0 positivecausing grid current to fiow. During the time grid current is flowing anegative voltage is built up across resistor I7 and this chargescondenser ll. When the anode current ceases increasing and begins todecrease, the transformer windings I8 and 12 drive the grid verynegative. The negative charge on the grid and condenser H leaks ofithrough resistors I! and I6, and no action takes place until the gridreaches a potential where anode current can again flow. Then the cycleof events is repeated, The time constant of condenser II and resistor l!is selected to give a frequency slightly lower than the sync frequency.Now if a positive voltage pulse from source S raises the grid voltage toa point where the anode current flows slightly earlier than if suchpulse were not applied, the pulse will trigger tube [0 and thereafterthe negative pulses (e-l) in its output circuit will be kept synchronouswith the source S. The resistance 11 may be made variable, if desired,to permit adjustment of the free oscillating period of tube ID; in whichevent the resistance is called a hold control. The output of tube I0 istransformed by windings l8 and 20 and impressed across the yoke winding2|, the polarities of the windin being such that the pulses make theupper end of winding 20 negative and start the retrace portion of thedeflection cycle. The anode of tube 25 is abruptly made negative at thistime, thereby making the tube non-conductive. By way of example, thenegative pulses (e2) may be about 1,000 to 4,000 volts. Each pulsestores energy in the yoke 22 as magnetic fiux and starts an oscillationthe frequency of which is determined by the inductance and distributedcapacity of yoke 22 and transformer l5. The oscillating current thusstarted lags the voltage by almost and provides the current change forretrace of the electron beam in kinescope 55. The other half of thefirst cycle of voltage oscillation makes the anode of tube 25 positiveand therefore conductive, which prevents the voltage from rising veryhigh in apositive direction. Instead, the current through tube 25charges the storage condenser 26 so that the side of the condenserconnected to the tube cathode is positive and the side of the condenserconnected to 3+ is negative. Thus tube 25 with condenser 26 acts as adamper for the oscillation in the yoke after the first halfcycle ofvoltage therein. The current in the yoke winding reaches a maximum whenthe voltage becomes approximately zero and then, instead of decreasingrapidly as in free oscillation, it decreases substantially linearly dueto charging condenser 26 at an almost constant potential. Any departurefrom linearity is corrected by adjusting the linearity control in thegrid circuit of tube 25. This controlled fiow of current (2') providesthe entire trace portion of the deflection cycle for kinescope 55 bymeans of its yoke 22.

After several cycles of operation the condenser 26'assumes anelectrostatic charge which is replenished during each conductive periodof. tube 25. Another important function of condenser 26 is to supplyanode current to tube l0 during the portion of the deflection cycle thatthe anode of tube 25 is negative and therefore non-conductive. Inasmuchas the D. C. anode circuits of tubes l6 and 25 are connected in series(as previously mentioned) tube l0 would be unable to draw its desiredmaximum current from the B supply if condenser 26 were not present. Afurther function of condenser 26 and tube 25 is to boost the anodevoltage applied to tube I 0, for it will be noted that the B supply andcharged condenser 26 are effectively in series in the anode currentcircuit of said tube. Thus the generation of each current pulse inprimary I8 is assisted, and its wave front steepened, by theelectrostatic charge stored in condenser 26 from a prior pulse.

During the portions of the deflection cycle that tube 25 is conductive,the anode current from the B+ terminal flows first through the centeringdevice 35, then through windings 20 and 2| to tube 25, from the cathodethereof through leads 38 and 39 to primary winding 98, thence to theanode of tube I0, and returns from the cathode of said tube to the 3-terminal. If an excess of average anode current in tube 25 is requiredit can be supplied by adjustment of the resistance 42 connected asshown. However, by usinglike tubes which preferably are high-currentlowimpedance power triodes and proper circuit design, the averageanode-currents will be substantially equal and therefore resistance 42maybe very high or eliminated. Also a twin power triode such as the6AS'7-G may be used.

The centering device 35 (by means of its taps 36 and 3'!) provides theusualv control. for centering the image in kinescope 55 in known manner.A width control for said tube may be provided by a variable inductance58 shunted across a portion of primary winding I8.

Referring specifically to Figure 1 it will be noted that the rectifiertube 41 has impressed upon it and condenser 50 the combined voltage oftransformer windings I2, 20, and 45, said windings being connected inseries relative to the rectified current. This current passes throughresistance I1 and the B supply as a connection from winding [2 towinding 20. If it is desired to omit the potential of winding [2, thepositive side of con denser 50 may be connected directly to ground ortap 36 or B-\-. The polarities of the connections just described aresuch that a high negative potential is developed in the lead 51 relativeto the remainder of the system. This potential is applied to thekinescope cathode 53. The second anode 56 is connected to a relativelypositive point in the system, such as 3+ or ground, thereby providingthe high D. C. potential required for operation of the kinescope. It isunderstood, of course, that the current required for such purpose isvery small.

Referring now to Figure 2, the high voltage for kinescope 55 is providedin a similar manner but it has a positive potential relative to theremainder of the system. In the Figure 2 arrangement the cathode 46 ofthe rectifier 41 is heated by separate filament winding 51. Theconnections of transformer windings 20 and 45 are reversed, that is,their outer ends are connected together instead of their adjacent endsas in Figure 1. Thus the negative pulses in primary l8 produce positivepulses at the end of winding 45 which is connected to anode 48 of therectifier. The filter condenser 50 is then charged by the rectifiedvoltage so that the side connected to cathode 46 is positive and theside connected to the upper end of winding 20 is negative. The highpositive D. C. potential thus obtained is applied through resistance 52to second anode 56 of kinescope 55, the cathode 53 of which may begrounded. Such connection adds the 13+ voltage to the rectified voltage.

While only two embodiments of the invention have been described andillustrated, it is obvious that many changes and substitutions can bemade within the purview of the invention and to meet particularrequirements.

What is claimed is:

1. The method for electromagnetically deflecting an electron beam whichcomprises, generating current pulses of short duration relative to adeflection cycle, storing energy from such a pulse as magnetic flux, andconverting said flux into electromagnetic deflection current at acontrolled rate continuously throughout the entire trace portion of saidcycle.

2. The method according to claim 1 including the steps of storing partof the energy of said deflection current as an electrostatic charge, andusing said charge in the generation of a succeeding current pulse.

3. The method for deflecting an electron beam which comprises,generating a current pulse and storing energy therefrom as magnetic fluxonly during the retrace portion of a deflection cycle, converting saidflux into deflection current at a controlled rate continuouslythroughout the entire trace portion of said cycle, converting a portionof said deflection current into an electrostatic charge, and using saidcharge at the start of the next retrace to assist in the generation ofthe next current pulse.

6 4. The method according to claim 3 wherein the current pulses aregenerated under direct control of positive sync pulses, and the leadingedges of said current pulses are steepened by said electrostatic charge.

5. A deflection system comprising electromagnetic means for deflectingan electron beam, means for generating a current pulse and energizingsaid electromagnetic means therewith during retrace of said beam, meansfor discharging the energy in said electromagnetic means, and means forcontrolling the rate of said discharge continuously during the entiretrace of saidbeam.

6. A deflection system according to claim 5 comprising in addition, acondenser connected to said discharging means, and means for partiallydischarging said condenser through said generating means to assist inthe generation of succeeding pulses.

'7. In a deflection system the combination of a first high-currentlow-impedance power tube having an anode and a cathode, a secondhighcurrent low-impedance power tube having an anode and a cathode, ananode-cathode circuit for each tube, a transformer coupling saidcircuits for periodic current, a source of anode voltage, said circuitsbeing connected in series across said source for direct current, and acondenser shunting the anode-cathode circuit of said second tube wherebysaid first tube is supplied with anode current when said second tube isnon-conductive.

8. The combination defined by claim '7 wherein each tube has a grid, andincluding a source of positive sync pulses connected to the grid andcathode of said first tube, and a linearity network connected to thegrid, anode, and cathode of said second tube.

9. In a deflection system including an electromagnetic deflection yokethe combination of a pair of high-current low-impedance power tubes,each having anode, cathode and grid electrodes, circuits for saidelectrodes, a source of anode voltage, one of said circuits being aseries circuit comprising three serially connected parts, said firstpart being the connection of said deflection yoke, from the positiveside of said source to the anode of one tube, said second part being,from the cathode of said one tube to the anode of the other tube, andsaid third part being, from the cathode of said other tube to thenegative side of said source; and a storage condenser connected betweenthe first and second parts of said series circuit such to embrace theseries connection of said deflection yoke and said one tube.

10. In a deflection system including an electromagnetic deflection yoke,the combination of, a first and second high current low impedance powertubes, said first tube having at least an anode, cathode, and controlelectrode, said second tube having at least an anode and a cathode, ablocking oscillator pulse generating circuit including said first powertube, a damper circuit including said second power tube, connectionsplacing the anode-cathode circuits of said power tubes in series withone another through said deflection yoke, and a storage capacitorconnected substantially in shunt with the series combination of saiddeflection yoke and said second discharge tube.

11. The combination defined by claim 10 including a transformer havingprimary and secondary windings, said primary being connected in theanode circuit of said first power tube, and

a magnetic deflection yoke having a winding connected across saidsecondary winding; said second power tube triode and said condenserbeing connected in series across said yoke winding.

12. The combination defined by claim 11 including a high-voltagesecondary winding on said transformer connected in series with the firstmentioned secondary winding, and a series-connected rectifier and filtercondenser connected across said secondary windings whereby theircombined voltage is rectified.

13. The combination defined by claim 12 including a third secondarywinding on said transformer connected in the control circuit of saidfirst power tube and in series with said first and high-voltagesecondary windings to add its voltage to the rectified voltage.

14. In a deflection system the combination of a first high-currentlow-impedance power tube having an anode and a cathode, a secondhighcurrent low-impedance power tube having an anode and a cathode, ananode-cathode circuit for each tube, a transformer having a primarywinding in the anode circuit of one said tube and a secondary winding inthe anode circuit of the other tube, a source of anode voltage, saidanode circuits being connected in series across said source, a condensershunting the anodecathode circuit of said second tube, a high-voltagesecondary winding on said transformer connected in series with the firstmentioned secondary winding, and a series-connected rectifier and filtercondenser connected across said secondary windings whereby theircombined'voltage is rectified.

15. The combination defined by claim 14 wherein said rectifier has acathode connected across a part of said high-voltage secondary windingat the high-voltage end thereof, whereby the rectified voltage has ahigh negative potential relative to the remainder of the system.

16. The combination defined by claim 14 in cluding a separate winding onsaid transformer, said rectifier having a cathode connected across saidseparate winding and having an anode connected to the high-voltage endof said highvoltage secondary winding, whereby the rectified voltage hasa high positive potential relative to the remainder of the system.

ALBERT W. FRIEND.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,382,822 Schade Aug. 14, 19452,383,333 Milward Aug. 21, 1945 FOREIGN PATENTS Number Country Date451,117 Great Britain July 29, 1936

